Mini fan

ABSTRACT

A mini-fan has a drive motor having an external rotor ( 222 ) and an internal stator ( 244 ). The external rotor ( 222 ) is equipped with a rotor shaft ( 234 ) that has a necked down portion ( 258 ) in the region of its free end ( 235 ). The mini-fan ( 216 ) has a bearing tube ( 238 ) on whose outer side the internal stator ( 244 ) is mounted and in whose interior is arranged a bearing arrangement ( 236 ) in which the rotor shaft ( 234 ) is rotatably supported. A closure arrangement ( 262 ) serves to close off the bearing tube ( 238 ) in liquid-tight fashion at one end, and is equipped, in the region of the necked down portion ( 258 ) of the rotor shaft ( 234 ), with at least one resilient securing member ( 260 ) that engages into that necked down portion ( 258 ) and secures the rotor shaft ( 234 ) against being pulled out of the bearing arrangement ( 236 ).

CROSS-REFERENCE

This application is a section 371 of PCT/EP2004/005017, filed 11 May2004, claiming priority from German applications DE 203 11 207, filed 16Jul. 2003 and DE 20 2004 005 341, filed 30 Mar. 2004, the disclosures ofwhich are hereby incorporated by reference.

FIELD OF THE INVENTION

The invention relates to a mini-fan. Such fans are also referred to asminiature or subminiature fans.

BACKGROUND

Mini-fans serve, for example, to cool processors in computers, for thecooling of small equipment items, etc. and have very small dimensions.For example:

fans of the ebm-papst 250 series have dimensions of 8×25×25 mm;

those of the ebm-papst 400F series, dimensions of 10×40×40 mm;

those of the ebm-papst 400 series, 20×40×40 mm; and

those of the ebm-papst 600 series, 25×60×60 mm.

The power consumption of such fans is 0.4-0.6 W for the 250 series,0.7-0.9 W for the 400F series, and 0.9-3.4 W for the 400 and 600 series.The weight is, for example, approximately 5 (five) grams for the 250series, between 17 and 27 g for the 400/400F series, and approximately85 g for the 600 series.

With fans of this miniature size, which must be very inexpensive, it isimportant to make assembly as simple as possible in order to enable ahigh level of automation during manufacture. Only extensive productionautomation additionally makes possible uniform quality in such fans,which is a prerequisite for a long average service life.

A complicating factor with such mini-fans is furthermore that theircomponents, entirely comparable to those of a mechanical watchmechanism, are very delicate and therefore not robust. The rotor shaft,for example, is often only as thick as a knitting needle, and cantherefore easily be bent if handled carelessly, rendering the fanunusable. This danger exists in particular during the assembly of such amini-fan, for example when it must be acted upon by a force for assemblypurposes.

SUMMARY OF THE INVENTION

An object of the invention is therefore to make available a novelmini-fan. According to the invention, this object is achieved byconfiguring the fan motor with an internal stator and external rotor,the rotor being rotatably supported in a bearing tube equipped with aclosure arrangement which closes off one end of the bearing tube in aliquid-tight manner, and includes at least one resilient securing memberto engage into a necked down portion of the rotor shaft and thereby keepthe rotor shaft from being pulled out of the bearing.

What is thereby achieved, with simple means, is a secure, liquid-tightjoin between the bearing tube and the closure arrangement. Because theinvention makes it possible to assemble the internal stator while it isstill separate from the rotor, and because the internal stator is asubstantially more robust component than the external rotor, the dangerof damage during the assembly operation is substantially reduced. In thecontext of a mini-fan according to the present invention, it istherefore possible first to assemble the internal stator; and once thelatter has been, for example, soldered in place on a circuit board, therotor can then very easily be installed and at the same time secured, byway of the at least one resilient securing member, against beinginadvertently pulled out.

Further details and advantageous refinements of the invention areevident from the exemplifying embodiments, in no way to be understood asa limitation of the invention, that are described below and depicted inthe drawings.

BRIEF FIGURE DESCRIPTION

FIG. 1 is a greatly enlarged longitudinal section through a mini-fanaccording to a preferred embodiment of the invention; for illustrationonly, a one-centimeter length is indicated for comparison, although thesize of the fan can of course fall within the limits typical for suchminiature and subminiature fans;

FIG. 2 is an even greater enlargement to explain the lubricantcirculation in the bearing arrangement with plain bearing that isdepicted;

FIG. 3 depicts one possible variant for connecting the stator winding ofthe external-rotor motor according to FIGS. 1 and 2 to a circuit board;

FIG. 4 is a very greatly enlarged longitudinal section through amini-fan according a second embodiment of the invention;

FIG. 5 shows a portion of FIG. 4 at location V therein;

FIG. 6 is a section according to a first alternative, looking along lineVI-VI of FIG. 4;

FIG. 7 is a section according to a second alternative, looking alongline VI-VI of FIG. 4;

FIG. 8 is a section analogous to FIG. 4, but after the mating of theinternal stator and circuit board;

FIG. 9 is a depiction analogous to FIG. 8, but before the mating of theinternal stator and external rotor; and

FIG. 10 is a depiction analogous to FIG. 9, but after the mating of theinternal stator and external rotor; the external rotor is secured on theinternal stator against being pulled out, and the lower (in FIG. 10)side of the bearing support tube is closed off in liquid-tight fashion.

DETAILED DESCRIPTION

FIG. 1 shows, at very greatly enlarged scale, a longitudinal sectionthrough a mini-fan 16 associated with which, for driving thereof, is anexternal-rotor motor 20. Fan 16 can have, for example, dimensions of10×30×30 mm. Motor 20 has an external rotor 22 having a rotor cup 24,preferably made of a thermally conductive plastic, on whose outerperiphery fan blades 26 are provided. A magnetic yoke 27 made of softiron is mounted in rotor cup 24, and on the yoke's inner side is aradially magnetized rotor magnet 28 that can be magnetized, for example,with four poles. The outside diameter of external rotor 22 can range,for example, from approximately 14 to approximately 35 mm.

Fan 16 is depicted here as an axial fan, but the invention is equallyapplicable, for example, to diagonal fans and to radial fans.

Rotor cup 24 has at its center a hub 30 in which is mounted, inthermally conductive fashion by plastic injection molding, acorrespondingly shaped upper shaft end 32 of a rotor shaft 34 whoselower, free end is labeled 35.

Radial support of shaft 34 is provided by a plain bearing 36 thatpreferably is implemented as a sintered bearing. Alternatively in thecontext of the invention, in order to achieve a particularly longservice life, shaft 34 can also be supported using rolling bearings.Plain bearing 36 is mounted by being pressed into the interior of aconstriction 37 of a bearing tube 38. Bearing tube 38 is preferablymanufactured from steel, brass, or another suitable metal, or ifapplicable also from a plastic. Provided at its lower end is a radialprojection in the form of a flange 39, which serves for the mounting offan 16 and here extends approximately perpendicular to rotation axis 41of rotor 22. Internal stator 44 of motor 20 is mounted on the outer sideof bearing tube 38 by being pressed on.

Constriction 37 has a substantially cylindrical inner side 40 (FIGS. 2and 3) whose surface is particularly carefully machined, while theremainder of the inner side of bearing tube 38 needs to be only roughlymachined. Corresponding to constriction 37, sintered bearing 36 has abulging portion 42 having a diameter that corresponds approximately tothe diameter of inner side 40 and is dimensioned so that a tight fitresults upon assembly in inner side 40. Within portion 42, sinteredbearing 36 has a portion 43 (FIG. 2) having an enlarged diameter, atwhich the sintered bearing does not make contact against shaft 34. Thisprevents sintered bearing 36 from being excessively radially compressedin the event of an accumulation of unfavorable tolerances, which mightmake it impossible to insert shaft 34.

A lower plain bearing portion 48 is located below portion 43, and anupper plain bearing portion 50 is located above portion 43 (cf. FIG. 2).It has been found that specifically in mini-fans with their smalldimensions, very reliable support of shaft 34, and a correspondinglylong service life for motor 20, are thereby obtained.

1. A mini-fan that comprises: a drive motor having an external rotor(222) and an internal stator (244), which external rotor is equippedwith a rotor shaft (234) that is equipped with a necked down portion(258) adjacent its free end (235); a bearing tube (238) on whose outerside the internal stator (244) is mounted, and in whose interior isarranged a bearing arrangement (236) in which the rotor shaft (234) isrotatably supported; a closure arrangement (62; 262) that closes off thebearing tube (238) in liquid-tight fashion at one end, and is equippedadjacent the necked down portion (258) of the rotor shaft (234) with atleast one resilient securing member (260) that engages into that neckeddown portion (258) of the rotor shaft (234) and secures the rotor shaft(234) against being pulled out of the bearing arrangement (236).
 2. Themini-fan according to claim 1, wherein the closure arrangement isimplemented as a cover (62) that is made from a thermoplastic that is atleast partially transparent to laser light, that cover (62) beingattached by means of a substantially liquid-tight welded join (100,102).
 3. The mini-fan according to claim 2 which comprises a housinghaving a flange (78); and wherein the welded join (100, 102) is providedat a location at which the cover (62) at least partly overlaps a portionof that flange (78).
 4. The mini-fan according to claim 2, which furthercomprises a housing having a flange (78), wherein the bearing tube (38)is held between the closure arrangement implemented as a cover (62) anda portion of that flange (78).
 5. The mini-fan according to claim 2,wherein the bearing tube (38) is pressed in substantially liquid-tightfashion into an opening (80) formed in the flange (78).
 6. The mini-fanaccording to claim 5, wherein the bearing tube (38) consists essentiallyof metal, and is epilam-coated on its side that is pressed into theflange opening (80).
 7. The mini-fan according to claim 3, wherein thebearing tube (38) is equipped with a radial projection (82) that is heldin positively engaged fashion between the closure arrangement (62) and aportion of the flange (78).
 8. The mini-fan according to claim 7,wherein the radial projection is implemented as a flange (82).
 9. Themini-fan according to claim 8, wherein the flange (82) is provided on anend portion of the bearing tube (38).
 10. The mini-fan according toclaim 1, wherein the rotor shaft (34; 234) comprises a free end (35;235), facing away from the rotor (22; 222), on which a tracking cap (68;268) is formed for axial support; and wherein a support surface (66;266) for that tracking cap is provided on the closure arrangement (62;262).
 11. The mini-fan according to claim 10, wherein the supportsurface is implemented as a depression (66; 266) and is equipped with alubricant (110).
 12. The mini-fan according to claim 1, wherein the atleast one resilient securing member (60; 260) protrudes into the neckeddown portion (58; 258) of the rotor shaft (34; 234) without touching it.13. The mini-fan according to claim 12, wherein there is provided,adjacent the free end of the shaft (34; 234), a spreading member (35;235) that is implemented to deflect the at least one resilient securingmember (60; 260) in a radial direction upon installation of the shaft(34; 234).
 14. The mini-fan according to claim 10, wherein the trackingcap (68; 268) is acted upon by a magnetically generated force urgingsaid rotor shaft in a direction toward the closure arrangement (62;262).
 15. The mini-fan according to claim 1, wherein the closurearrangement is implemented as a plug that is mounted in an opening ofthe bearing tube.
 16. The mini-fan according to claim 15, wherein theclosure arrangement is pressed in liquid-tight fashion into the openingof the bearing tube (238).
 17. The mini-fan according to claim 15,wherein at a transition point (271, 283) between the bearing tube (238)and plug (262), there is implemented on one of those parts an annularridge (284, 285) and on the other part an annular groove (272, 273)complementary thereto, which together form a latching connection whenthe plug (262) is installed.
 18. The mini-fan according to claim 15,wherein the bearing tube (238) has a larger inside diameter at itsportion (271) provided for reception of the plug (262) than at itsportion (240) provided for reception of the bearing arrangement (236).19. The mini-fan according to claim 1, wherein the bearing tube (238)comprises a portion (278) that protrudes away from the rotor (222) andis implemented for installation in an opening (280) of a component(217).
 20. The mini-fan according to claim 1, wherein the internalstator (44; 244) comprises a lamination stack (45; 245) on which isarranged a coil former (46; 246) having a stator winding (247), andmounted on that coil former is at least one rigid electrical conductor(132; 288) that is electrically connected to the stator winding (247)and extends substantially parallel to the rotation axis (41; 241) of themini-fan.
 21. The mini-fan according to claim 20, wherein the bearingtube (238) comprises an outwardly protruding flange (239) that isequipped with an orifice (292) for the passage of the rigid electricalconductor (288).
 22. The mini-fan according to claim 1, wherein theinternal stator (44; 244) comprises a lamination stack (45; 245) and theexternal rotor (22; 222) comprises a permanent magnet (28; 228) coactingwith the internal stator, which magnet is offset relative to thelamination stack (45; 245) of the internal stator (44; 244) in such away that a magnetic force is generated which acts upon the tracking cap(68; 268) in a direction toward the support surface (66; 266).
 23. Themini-fan according to claim 1, wherein an end portion (32; 232) of theshaft (34; 234) is joined to a fan wheel (26; 226); and near atransition from the shaft (34; 234) to the fan wheel (26; 226); asurface (112; 312) is provided which extends approximately radially andis located inside the bearing tube (38; 238), so that lubricant (110)thrown off from that surface upon rotation of the fan wheel is throwninto the interior of the bearing tube (38; 238).
 24. The mini-fanaccording to claim 23, wherein the approximately radially extendingsurface (112; 312) is implemented in undercut fashion.
 25. The mini-fanaccording to claim 23, wherein the bearing tube (38; 238) comprises, inthe region of its end facing away from the cover (62; 262), an inwardlyprotruding portion (114; 314).
 26. The mini-fan according to claim 25,wherein the inwardly protruding portion (114; 314) is separated from thefan wheel (26; 226) at least locally by a gap (116; 316) that isimplemented in the manner of a capillary gap, in order to reduce theemergence of lubricant (110) through that gap.
 27. The mini-fanaccording to claim 25, wherein the inwardly protruding portion isimplemented, on its side facing toward the closure arrangement (62;262), in the manner of an undercut (114; 314).
 28. The mini-fanaccording to claim 1, wherein a sintered bearing (36; 236) is providedin order to support the shaft (34; 234), which bearing is arranged inthe bearing tube (38; 238) that comprises on its inner side a portion(138) of reduced diameter, for reception of the sintered bearing (36;236).
 29. A mini-fan having a housing (74) that is equipped with aflange portion (78) that in turn comprises a flange opening (80), havinga cover (62) for closing off that flange opening (80), further having ajoin (100, 102) provided between the flange portion (78) and the cover(62), and having a bearing tube (38) in which a bearing arrangement (36)for a shaft (34) of the fan is located; the bearing tube (38) being heldin positively engaged fashion between the cover (62) and flange portion(78).
 30. The mini-fan according to claim 29, wherein the bearing tube(38) is pressed in substantially liquid-tight fashion into the flangeopening (80).
 31. The mini-fan according to claim 29, wherein thebearing tube (38) is equipped with a flange (39) that is held inpositively engaged fashion between the cover (62) and the flange portion(78).
 32. The mini-fan according to claim 29, wherein the join betweenthe flange portion (78) and cover (62) is implemented as a welded join(100, 102).
 33. The mini-fan according to claim 29, wherein the shaft(34) of the fan comprises a free end (35); and a holding apparatus (60)that is implemented to retain that free end (35) is provided on thecover (62).
 34. The mini-fan according to claim 29, wherein the shaft(34) of the fan has a free end (35) that is equipped with a tracking cap(68) associated with which is a corresponding depression (66) in thecover (62), which depression forms, together with the tracking cap (68),a bearing for the shaft (34).
 35. The mini-fan according to claim 5,wherein the bearing tube (38) is formed with a constriction (37) inwhich a sintered bearing (36) is mounted.
 36. The mini-fan according toclaim 35, wherein the inner side (40) of the constriction (37) has abetter-machined surface than other, unconstricted portions of the innerside of the bearing tube (38).
 37. A mini-fan, having a fan wheel (22)that is equipped with a shaft (34) for support thereof, having asintered bearing (36) to support that shaft (34), having a bearing tube(38) for reception and retention of the sintered bearing (36), whichbearing tube comprises, on its inner sides a portion (37) having areduced inside diameter, in which portion the sintered bearing (36) ismounted.
 38. The mini-fan according to claim 37, wherein the sinteredbearing (36) comprises a portion (42) having an enlarged outsidediameter, which outside diameter corresponds approximately to thereduced inside diameter of the bearing tube (38) in order to permitmounting of the sintered bearing (36) in the bearing tube (38) in theregion of that portion (42) having an enlarged outside diameter.
 39. Themini-fan according to claim 37, wherein the bearing surfaces (48, 50) ofthe sintered bearing (36) are located substantially outside the portion(42) having an enlarged inside diameter.
 40. The mini-fan according toclaim 37, wherein the bearing surfaces (48, 50) of the sintered bearing(36) are located substantially at locations that are located outside thelocations at which the sintered bearing (36) is held in the bearing tube(38).
 41. The mini-fan according to claim 37, wherein the shaft (34)comprises a free end (35) facing away from the fan wheel (22), and nearthis free end (35), at least one closure member (62) is provided whichseals that end (39) of the bearing tube (38) in substantiallyliquid-tight fashion.
 42. The mini-fan according to claim 41, wherein alubricant supply (64) is provided in the region of the sealed end (39)of the bearing tube (38).
 43. The mini-fan according to claim 41,wherein the shaft (34) is equipped in the region of its free end (35)with a tracking cap (68), associated with which in the closure member(62) is a corresponding running surface (66) that, together with thetracking cap (68), forms an axial bearing for the shaft (34).
 44. Themini-fan according to claim 37, wherein the shaft (34) comprises a freeend (35) facing away from the fan wheel (22), and in the region of thatfree end (35) an annular groove (58) is provided into which protrudes,in the assembled state, a resilient latching member (60) that ismechanically connected to the housing of the mini-fan and counteractspulling of the installed shaft (34) out of the sintered bearing (36).45. The mini-fan according to claim 44, wherein the resilient latchingmember (60) is implemented integrally with a closure member (62) whichserves to close off the bearing tube (38) in substantially liquid-tightfashion.